Owner

Current status

Detailed Description

The GNU C Library version 2.26 will be released at the beginning of August 2017; we have started closely tracking the glibc 2.26 development code in Fedora Rawhide and are addressing any issues as they arise. Given the present schedule Fedora 27 will branch after the GLIBC 2.26 upstream release. However, the mass rebuild schedule means Fedora 27 will mass rebuild just after GLIBC 2.26 upstream freezes ABI for release, so careful attention must be paid to any last minute ABI changes.

Benefit to Fedora

Stays up to date with latests security and bug fixes from glibc upstream.

Scope

Proposal owners: Update glibc to 2.26 from tested upstream release.

Other developers: Developers need to ensure that rawhide is stable and ready for the Fedora 27 branch. Given that glibc is backwards compatible and we have been testing the new glibc in rawhide it should make very little impact when updated.

Release engineering: [1] All Fedora releases must be released using a released version of glibc. The Fedora glibc team is responsible for ensuring that Fedora Rawhide stabilizes ABI before a Fedora release, or that after the branch that the Fedora release is rebased (a very small rebase) to the final released version. This is a requirement for Fedora to inherit the ABI and API guarantees provided by upstream. If a mass rebuild is required by glibc or other components, the Fedora glibc team will ensure coordination with release engineering such that a mass rebuild uses the released version of glibc to fix any last minute ABI changes. The GNU C Library (glibc) does not require a mass rebuild for this release.

Upgrade/compatibility impact

We fully expect to fix all packaging changes in Fedora Rawhide given that glibc in Rawhide is tracking what will become glibc 2.26.

How To Test

The GNU C Library has its own testsuite, which is run during the package build and examined by the glibc developers before being uploaded. This test suite has 2500+ tests that run to verify the correct operation of the library. In the future we'll also be running the microbenchmark to look for performance regressions as well as behavioural ones.

User Experience

Users will see improved performance, many bugfixes and improvements to POSIX compliance, additional locales, etc. The glibc 2.26 NEWS update will include more details.

Dependencies

All packages do not need to be rebuilt, but for IBM POWER, particularly ppc64le we will be migrating from a long double that uses IBM double-double format to IEEE-754 128-bit long double. This is an ABI transition for ppc64le and will be backwards compatible, but the two ABIs will not interoperate, so an application needs to choose one or the other.

Contingency Plan

Contingency mechanism: Given that Rawhide has started tracking GLIBC 2.26, no show-stopper problems are expected. At this point, we can still revert to upstream version 2.25 if insurmountable problems appear, but to do so may require a mass rebuild to remove new symbols from the ABI/API.

Contingency deadline: Upstream ABI freeze deadline of 2017-07-01.

Blocks release? Upgrading glibc does block the release. We should not ship without a newer glibc, there will be gcc and language features that depend on glibc being upgraded. Thus without the upgrade some features will be disabled or fall back to less optimal implementations.

Documentation

The glibc manual contains the documentation for the release and doesn't need any more additional work.